Manufacturing method of unfired basic brick

Abstract

To provide a manufacturing method of an unfired basic brick substantially free of a carbonaceous raw material, which can improve hardness thereof in an intermediate temperature range of around 1000°C.SOLUTION: A refractory raw material compound including at least one kind selected from magnesia clinker and magnesia-chrome clinker in a sum total of 40 mass% or over and 99 mass% or under, and at least one kind selected from calcium sulfate 0.5-hydrate, calcium sulfate dihydrate, and calcium sulfate anhydride in a sum total of 1 mass% or over and 10 mass% or under in a calcium sulfate anhydride conversion value, and a carbonaceous raw material of 1 mass% or under (including 0) is mixed, molded under pressure, and heated at 60°C or over and 1000°C or under.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing unfired basic bricks that are substantially free of carbonaceous raw materials such as unfired magnesia-chrome bricks and unfired magnesia bricks, which are used in molten metal containers and secondary refining furnaces in the steel field and the like. In this specification, "unfired basic bricks substantially free of carbonaceous raw materials" refers to those having a carbonaceous raw material content rate of 1% by mass or less (including 0) in the refractory raw material blend.

Background Art

[0002] For molten metal containers used in the steel field and the like, basic bricks such as magnesia-chrome bricks, magnesia bricks, and magnesia-carbon bricks are widely used as linings. Among these, magnesia-carbon bricks are generally unfired bricks containing carbonaceous raw materials such as graphite and using organic binders such as phenolic resins as binders. However, in applications where the loss due to oxidation is large, fired basic bricks such as magnesia-chrome bricks and magnesia bricks that substantially do not contain carbonaceous raw materials such as graphite are frequently used. Among them, fired magnesia-chrome bricks develop secondary spinel containing chromium by high-temperature firing at 1700 °C or higher, and have high corrosion resistance by forming a direct bond. On the other hand, fired basic bricks also have demerits such as CO2 emissions during production and cost increases.

[0003] Therefore, methods for producing unfired basic bricks that are substantially free of carbonaceous raw materials such as unfired magnesia-chrome bricks and unfired magnesia bricks have been studied. However, in these unfired bricks that are often used in an oxidizing atmosphere, carbon bonding by phenolic resins or pitch, and further strength imparting by metal carbides generated by heating cannot be expected. Therefore, there has been a problem that the strength in the intermediate temperature range around 1000 °C is insufficient.

[0004] On the other hand, a binder mainly composed of an inorganic compound may be used. For example, Patent Document 1 discloses "an unburned magnesia-carbon refractory characterized by adding a binder prepared by blending at least one of bitter juice or an aqueous magnesium sulfate solution into a phenolic resin having the property of dissolving in an equal amount of water." This unburned magnesia-carbon refractory is a so-called magnesia cement-bonded brick, and magnesium oxychloride or magnesiumoxysulfate constituting the magnesia cement is decomposed by heating because it is formed by a mineral phase containing crystal water. Therefore, even in the unburned magnesia-carbon refractory of Patent Document 1, there was a problem that the strength in the intermediate temperature range around 1000 °C was insufficient.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem to be solved by the present invention is to provide a method for producing an unburned basic brick that can improve the strength in the intermediate temperature range around 1000 °C in an unburned basic brick that substantially does not contain a carbonaceous raw material.

Means for Solving the Problems

[0007] According to one aspect of the present invention, a method for producing the following unburned basic brick is provided. A method for manufacturing unfired basic bricks, comprising kneading a refractory raw material composition containing at least one of magnesia clinker and magchrome clinker in a total amount of 40% by mass or more and 99% by mass or less, and at least one of calcium sulfate hemihydrate, calcium sulfate dihydrate, and anhydrous calcium sulfate in a total amount of 1% by mass or more and 10% by mass or less in terms of anhydrous calcium sulfate, and having a carbonaceous raw material content of 1% by mass or less (including 0), followed by pressure molding and heat treatment at 60°C or higher and 1000°C or lower.

Advantages of the Invention

[0008] The unfired basic bricks obtained by the manufacturing method of the present invention have improved strength in the intermediate temperature range around 1000°C, and thus have improved durability compared to conventional unfired basic bricks.

Embodiments for Carrying Out the Invention

[0009] Magnesia (MgO) and magchrome (MgO·Cr2O3) are high melting point substances with melting points of about 2800°C and about 2400°C respectively, and it is not possible to expect strength imparted by sintering around 1000°C. In contrast, calcium sulfate (CaSO4) has a relatively low melting point of 1460°C, and it has been found that sintering occurs even around 1000°C. Therefore, it is considered that the strength in the intermediate temperature range around 1000°C is improved by containing calcium sulfate. Among calcium sulfates, the one with hydraulicity is hemihydrate (bassanite), but the calcium sulfate that can be used in the present invention is not limited to this, and dihydrate (gypsum) and anhydrous (anhydrite) can also be used, and like hemihydrate, they are effective for imparting strength in the intermediate temperature range around 1000°C. That is, by using other binders such as saccharides and phenolic resins in combination, the normal temperature strength of the substrate is imparted, so that anhydrous and dihydrate without hydraulicity can be used.

[0010] In the present invention, the content of calcium sulfate (at least one of hemihydrate, dihydrate, and anhydride) in the refractory raw material composition needs to be 1% by mass or more and 10% by mass or less in terms of the total value of anhydrous calcium sulfate (CaSO4). If the content is less than 1% by mass, the sintering promotion in the intermediate temperature range around 1000°C will be insufficient, and a predetermined strength cannot be obtained. If it exceeds 10% by mass, the structure near the working surface will become porous due to the thermal decomposition of calcium sulfate, and the corrosion resistance will decrease.

[0011] The calcium sulfate hemihydrate that can be used in the present invention is generally called "calcined gypsum", and those generally commercially available as ceramic raw materials or for arts and crafts can be used. As the calcium sulfate dihydrate, those generally commercially available for food or cosmetics can be used. As the anhydrous calcium sulfate, those obtained by firing the hemihydrate or dihydrate at 300 to 700°C can be used. From the viewpoint of uniformly dispersing these calcium sulfates (at least one of hemihydrate, dihydrate, and anhydride) in the refractory raw material composition, it is preferable that the particle size is fine. For example, the particle size can be less than 0.1 mm. Here, the particle size referred to in the present invention is the size of the sieve mesh when the refractory raw material particles are sieved and separated. For example, calcium sulfate with a particle size of less than 0.1 mm means calcium sulfate that passes through a sieve with a mesh size of 0.1 mm, and calcium sulfate with a particle size of 0.1 mm or more means calcium sulfate that does not pass through a sieve with a mesh size of 0.1 mm.

[0012] The unfired basic bricks targeted by the present invention are those obtained by making conventional fired magnesia bricks and fired magnesia chrome bricks unfired, and contain at least one of magnesia clinker and magnesia chrome clinker in a total amount of 40% by mass or more and 99% by mass or less in the refractory raw material composition. If the content is less than 40% by mass, the corrosion resistance of the bricks to basic slag will be insufficient. If it exceeds 99% by mass, the content of calcium sulfate will be insufficient, resulting in insufficient strength in the intermediate temperature range around 1000°C.

[0013] As the magnesia clinker and the magnesia-chrome clinker used in the present invention, those generally used as refractory raw materials such as magnesia bricks, magnesia-carbon bricks, or magnesia-chrome bricks can be used. Note that the particle sizes of the magnesia clinker and the magnesia-chrome clinker may also be general ones. For example, within the range of particle size less than 5 mm, coarse particles, medium particles, and fine particles can be appropriately used.

[0014] In the present invention, it is also possible to use refractory raw materials other than magnesia clinker, magnesia-chrome clinker, and calcium sulfate in combination. For example, chromite, chromium oxide, spinel clinker, alumina, dolomite, aluminum, silicon, ferrochrome, etc. can be mentioned, but it is not limited thereto. Also, refractory raw materials obtained by means such as mixing and melting refractory raw materials other than magnesia with magnesia can be used in the same manner.

[0015] Since the unburned basic brick of the present invention is often used in an oxidizing atmosphere, it does not substantially contain a carbonaceous raw material in its refractory raw material formulation. That is, in the present invention, the content rate of the carbonaceous raw material in the refractory raw material formulation is 1 mass% or less (including 0). Examples of the carbonaceous raw material include graphite, coke, carbon black, pitch powder, etc.

[0016] The unburned basic brick of the present invention can be obtained by kneading a refractory raw material formulation containing at least one of magnesia clinker and magnesia-chrome clinker, and at least one of calcium sulfate hemihydrate, calcium sulfate dihydrate, and anhydrous calcium sulfate, followed by pressure molding and heat treatment at 60°C or higher and 1000°C or lower. During kneading, in the same manner as the kneading method of the refractory raw material formulation in the general refractory manufacturing method, an appropriate amount of a binder, water, an organic solvent, etc. is added and kneaded to obtain good moldability. Also, the heat treatment temperature may be any temperature from 60°C to 1000°C depending on the use conditions.

[0017] In the present invention, when kneading a refractory raw material composition, a binder capable of developing strength by subsequent pressure molding and heat treatment can be used. Any such binder that is generally used as a binder for unburned bricks can be used without problems. For example, one or more of silicates, phosphates, silica fine powder, phenolic resins, magnesium chloride, magnesium sulfate, molasses, and sugar alcohols can be used. Note that calcium sulfate hemihydrate can obtain sufficient strength after pressure molding and heat treatment by the hydraulicity of gypsum without using a special binder by adding water during kneading, and also exhibits the function as a binder.

Examples

[0018] Table 1 shows the compositions of the refractory raw material compositions in the examples and comparative examples of the present invention, and the evaluation results of the obtained bricks.

[0019]

Table 1

[0020] Among the refractory raw materials shown in Table 1, as magnesia clinker, fused magnesia with a MgO purity of 98% by mass was used, as magnesia chrome clinker, fused magnesia chrome with 74% by mass of MgO and 16% by mass of Cr2O3 was used, and as chromite, the one with 55% by mass of Cr2O3, 14% by mass of Fe2O3, 16% by mass of MgO, and 11% by mass of Al2O3 was used. Also, as spinel clinker, the one with 75% by mass of Al2O3 and 25% by mass of MgO was used, as chromium oxide, the one with a Cr2O3 purity of 99% by mass was used, and as alumina, sintered alumina with an Al2O3 purity of 98% by mass was used. In addition, as calcium sulfate dihydrate, a commercially available product as a food additive was used, as calcium sulfate hemihydrate, a commercially available product generally called "calcined gypsum" for arts and crafts was used, and as anhydrous calcium sulfate, the calcium sulfate dihydrate heat-treated at 600°C for 3 hours was used. Note that the particle sizes of these calcium sulfates were all less than 0.1 mm in particle diameter. Among the additives added during kneading, a 70% solution of D-sorbitol was used as the sugar alcohols. In Table 1, the addition rate of the additives is shown as the addition rate (mass%) based on 100% by mass of the refractory raw material formulation.

[0021] Additives were added to the refractory raw material formulations shown in Table 1 and kneaded to obtain green bodies, which were then die-molded at a molding pressure of approximately 100 MPa. The molded bodies were heat-treated at 110°C for 24 hours to remove unnecessary solvents and ensure the strength required during handling. The samples of each example thus obtained were cut into a predetermined shape, and the flexural strengths at room temperature and 1000°C were measured in accordance with JIS R 2213 and JIS R 2656, respectively. The corrosion resistance was evaluated by lining the inner surface of a high-frequency induction furnace with multiple types of bricks (samples), melting steel, adding synthetic slag thereon, and corroding the lined bricks (samples). The test conditions were 1700°C for 5 hours, and the CaO / SiO2 ratio of the slag was 3.0. The corrosion resistance evaluation test was conducted multiple times. After the test, the samples were cut longitudinally, and the maximum wear thickness of the cross-section was measured and shown as a corrosion loss index with Comparative Example 1 taken as 100. The smaller this corrosion loss index, the better the corrosion resistance.

[0022] Examples 1 to 6 involve different types and contents of calcium sulfate used, but all are within the scope of the present invention. The hot flexural strength at 1000°C is sufficient, and the corrosion resistance also shows good results. In contrast, Comparative Example 1 does not contain calcium sulfate, resulting in a lower hot flexural strength at 1000°C. On the other hand, Comparative Example 2 has a calcium sulfate content exceeding the upper limit of the present invention, resulting in a decrease in corrosion resistance. Example 7 is a direct bond type magnesia-chrome brick, Example 8 is a spinel magnesia brick, Example 9 is a ribbond type magnesia-chrome brick, and Example 10 is a magnesia-alumina brick. All are within the scope of the present invention, and both the flexural strength and corrosion resistance show good results.

Claims

【Claim 1】 A method for producing unfired basic bricks, comprising kneading a refractory raw material composition containing at least one of magnesia clinker and magchrome clinker in a total amount of 40% by mass or more and 99% by mass or less, and at least one of calcium sulfate hemihydrate, calcium sulfate dihydrate, and anhydrous calcium sulfate in a total amount of 1% by mass or more and 10% by mass or less in terms of anhydrous calcium sulfate, and having a carbonaceous raw material content of 1% by mass or less (including 0), followed by pressure molding and heat treatment at 60°C or higher and 1000°C or lower.

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